1. Field of the Invention
The present invention relates to a voltage supply circuit for efficiently supplying a power voltage to an amplifier.
2. Description of Related Art
There is a known voltage supply circuit of high efficiency that is designed to switch a power voltage supplied to an amplifier between a low voltage V.sub.L and a high voltage V.sub.H in accordance with the level of the amplifier's output signal. If the level of the output signal of the amplifier goes up to exceed a predetermined threshold value when the low voltage V.sub.L is supplied as the power voltage, the high efficiency voltage supply circuit switches the power voltage supplied to the amplifier from the low voltage V.sub.L to the high voltage V.sub.H. Conversely, if the level of the output signal of the amplifier falls below a predetermined threshold value when the high voltage V.sub.H is supplied, the circuit switches the power voltage from the high voltage V.sub.H to the low voltage V.sub.L.
Generally, a power circuit for generating the low voltage V.sub.L and high voltage V.sub.H for the amplifier does not generate precisely stabilized voltages. The level of the power voltage fluctuates in each of the low voltage V.sub.L and high voltage V.sub.H in accordance with the magnitude of current supplied to the amplifier, because of an influence of the internal resistance of the power source circuit. In an extreme case, if a loudspeaker is disconnected from the amplifier when the high voltage V.sub.H is supplied, then a maximum voltage that is obtainable as the high voltage V.sub.H will be applied as the power voltage due to a decrease in the supply current. Therefore, it is necessary to use electric parts of the amplifier such as a capacitor or the like, which have a relatively high withstanding voltage.